Tests

feat: `double` method for `FieldElement` #1078

Job	Run time
no-std build	1m 27s
no-std build	1m 27s
Windows tests (stable, x86_64-pc-windows-gnu)	13m 56s
Windows tests (stable, x86_64-pc-windows-gnu)	13m 56s
WASM tests	3m 48s
WASM tests	3m 48s
Unix tests (ubuntu-latest, stable)	1m 44s
Unix tests (ubuntu-latest, stable)	1m 44s
Windows tests (stable, x86_64-pc-windows-msvc)	10m 42s
Windows tests (stable, x86_64-pc-windows-msvc)	10m 42s
Unix tests (ubuntu-latest, nightly)	12m 26s
Unix tests (ubuntu-latest, nightly)	1m 52s
Windows tests (nightly, x86_64-pc-windows-gnu)	4m 35s
Windows tests (nightly, x86_64-pc-windows-gnu)	4m 35s
Unix tests (macos-11, stable)	12m 26s
Unix tests (macos-11, stable)	13m 13s
Windows tests (nightly, x86_64-pc-windows-msvc)	14m 27s
Windows tests (nightly, x86_64-pc-windows-msvc)	13m 20s
Unix tests (macos-11, nightly)	7m 32s
Unix tests (macos-11, nightly)	7m 32s
	2h 35m 12s

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